Numerous polyester molding compositions are well known and widely used as a structural material in various articles of manufacture. Polyester/fiberglass composites are commonly employed as a substitute for metals in many applications. In some applications polyester/fiberglass composites exhibit properties that are superior to those of metals. For example, in applications that require high strength and light weight, such composites sometimes offer a very significant advantage. However, certain drawbacks have precluded polyester/fiberglass composites from being used in some applications. One of these drawbacks is the tendency for polyester/fiberglass composites to creep. Creep is especially troublesome in composite articles at elevated temperatures. Creep is the slow deformation of a material that is induced by a stress and which results in increasing strain.
Many attempts have been made to substitute polyester/fiberglass composites for the metal used in vehicle wheels. Unfortunately creep is a problem that cannot be tolerated in wheels which has precluded polyester/fiberglass composites from being a structural material that is totally satisfactory for use in this application. Creep normally cannot be tolerated in wheels since it causes the clamp torque between the fastener used to affix the wheel to a vehicle and the wheel to decrease. In other words, creep can result in the loosening of the lug nuts used to hold the wheel to the vehicle. Such a loss of torque is unsatisfactory since it could ultimately lead to unsafe vehicle performance. Shrinkage of composite materials at high temperatures is another problem that can cause such a loss of torque. Thus, materials that shrink at high temperatures are not acceptable for use as a material from which to make wheels. One approach to solving this problem is to control the arrangement of the fibers in the molded composites, particularly in the lug bolt hole area, see U.S. Pat. No. 4,294,490 which employs a paste of either an unsaturated polyester, a vinyl ester or an epoxy resin; a thickener, such as, a Group II metal oxide, hydroxides or alkoxides; a catalyst, such as, an organic peroxide or a hardner; an inert filler, such as, calcium carbonate or clay; and a mold release agent, such as, zinc stearate to mold the wheel containing the reinforcing fibers.